The present invention relates in general to means for controlling the bounce or rebound motion of an armature and finds use in high performance fuel injectors.
In general, a solenoid valve comprises an armature movable between first and second positions. The extremes of the these first and second positions are often defined by mechanical stops. Armatures, as is known in the art, are moved in one direction by a electro-magnetic force generated by a coil of wire and often moved in the opposite direction by a return spring. When the armature impacts a stop it bounces. Bounce or rebound is detrimental especially if the solenoid is to be used as a positioning device because desired position cannot be maintained, or if the solenoid is incorporated within a fuel injector wherein when the armature moves toward or away from a valve seat due to bounce or rebound more or less fuel, as the case may be, will be ejected from the fuel injector. The bouncing continues until the hysteresis losses in the armature and/or stop finally cause the armature to come to rest. As can be seen, the bounce of an armature effects the operation of a fuel injector by: prolonging or shorting the duration of injection, causing non-linearality in calibration, excessive wear about the valve seat area, poor and variable atomization of the ejected fuel, a lack of repeatability in the operation of the injector over its useful life and a cycle-to-cycle variation in the performance of the injector.
In view of the above, it is the primary object of the present invention to provide means for damping the motion of an armature to lessen and/or totally eliminate bounce. A further object of the invention is to eliminate bounce through the use of an energy absorbing device. A further object of the invention is to dampen armature motion by generating a viscous shear force.
Accordingly the invention comprises a mechanism for damping the motion of an armature and may be incorporated within an electro-mechanical fuel injector comprising: a housing and valve seat including a valve seating surface and a metering orifice disposed at a lower end of the housing. An armature assembly is movable relative to the valve seating surface for opening and closing, the metering orifice, and includes an armature and a Pin extending therefrom and adapted to engage the seating surface. The fuel injector additionally includes means for moving the armature assembly comprising: a coil assembly comprising a coil and a stator magnetically coupled therewith, and when activated operative to move the armature assembly in a direction to open the metering orifice; and bias means (46) for urging the armature assembly in a direction to close the metering orifice. A fluid chamber defined upstream of the metering orifice, in surrounding relation to a portion of the armature assembly; and means, are additionally provided, movable with the armature assembly, within the fluid chamber, for generating a viscous force to damp the motion of the pin by dissipating energy from a collision of said armature means with the seating surface.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.